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Full text of "Application of the principle of dispersion to Portland cement."

/ 3o4- 



RESEARCH PAPER NUMBER THIRTY-FIVE 



JUL 12 1942 

APPLICATION OF THE 

PRINCIPLE OF DISPERSION 

TO PORTLAND CEMENT 



I 



BY 

EDW. W. SCRIPTURE, JR. t PH.D. 

DIRECTOR 

Master Builders Rehe>trch Laboratories 
CLEVELAND, OHIO 



]W 



COPYRIGHT 1941 - THE MASTER BUILDERS COMPANY 



FOREWORD 



EXfilXEERS, architects and those connected with 
the various phases of construction are well ac- 
quainted with the many improvements made in the 
manufacture of Portland cement since its introduction. 
They are familiar with the facts that better design of 
mixes and more care in the selection of aggregates have 
vastly increased the quality of concrete and mortar. 
but i hey are also aware that an important problem 

o do with durability and the other prop* - 
of concrete remained to be solved: the redaction of 
watei necessary to place all concrete. Leading 
investigators have seen the vital need for this improve- 
ment while observing the performance of concrete 
during and after placement in many existing structures, 
and also in the upkeep costs of structural repairs 
of railroads, utilities and other large industrial 
organizations. 



The Researcn i^aDoraiory of The Master Builders 
Company recently announced a new principle for the 
improvement of concrete and mortar — Cement Dis- 
persion. They have spent ten years in proving that 
by adding to the concrete or mortar mix a < < 
dispersing agent the basic problem of all cement mixes 
is attacked, namely, tin excess water required for 
placeability. Reduction of this water insures improve- 
ment of the properties of the structure with respect 
to durability, watertightness, strength and other im- 
portant qualities. 



The Master Builders Company feeling 'that the 
introduction of this discovery and its application to 
practical construction will be welcomed by everyone 
connected with the building industry has published 
this paper. The following pages set forth the manner 
in which dispersing agents function in colloidal systems 
generally, and describe the way in which this principle 
has been applied to cement for the improvement of 
concrete and mortar. 



y 



APPLICATION OF THE 

PRINCIPLE OF DISPERSION 

TO PORTLAND CEMENT 

INTRODUCTION 

rjORTLAND Cement is an extremely versatile material admirably 
\ adapted to a great variety of applications. Its ability to be 
placed, mixed with aggregate, in the form of a plastic mass into 
anv desired shape and subsequently to harden in that shape make it 
a means for carrying out operations of construction which could not 
r^adilv be accomplished in any other way. Its low cost makes feasible 
structures which could not otherwise be attempted. 

In its very strength lies its greatest weakness. To make a plastic 
mass from portland cement and aggregate, either mortar or concrete. 
it is necessarv to add water. Part of this water is required to combine 
with the cement but the greater part of it serves no other purpose than 
to make the mix placeable as has been stated by Mr. P. H. Bates: — 

"Since the amount of water required to produce the hydration 
accompanying maximum development of strength is much less than 
that used 'in dry mixes of concrete somewhat less than 18 pounds of 
water per bag of cement are needed to produce a decidedly 'complete 
hydration": this is less than half the amount used in a 4.5 gallons per 
bae mix, usually considered a very dry mix , it can be realized that a 
very large part* of the mixing water should really be called 'placing 
water, and is needed to get the concrete to where it is desired that it 
should harden. We are, therefore, attaining a strength less than the 
potential strength and in so doing also materially affecting adversely 
the properties of volume change and durability." 

Manv attempts have been made to overcome the inherent dis- 
advantages from which portland cement suffers. These have taken 
various forms. Chemical reagents, such as calcium chloride, have been 
added to change the rate of the hydration reaction. Modifications have 
been made in the composition of the cement itself. In general such 
measures have produced certain results with respect to acceleration, 
retardation or similar properties but they have not had any significant 
effect in solving the basic problem of eliminating or reducing the excess 
water. In order to overcome the tendency, directly attributable to 
excess water, of the concrete to absorb water, waterproofing ingredients 
of the water-repellant or stearate type have been introduced. These 
have served a useful purpose under some conditions, particularly where 
no hydrostatic pressure was involved, but have not attacked the 

l Trends in the Production and Use of Various Types of Hydraulic Cements by 
P. H. Bates, J. Am. Con. Inst., Jan.-Feb. 1935. 

[4] 



fundamental problem. Pozzuolanic materials have been employed to 
improve corrosion resistance but these have had to compete with the 
increase in water necessitated by their addition to the mix. Other 
finely divided powders have been incorporated in concrete mixes for 
reasons which were not always clear but usually with the idea that 
workability would be improved. Such materials defeat their own 
purpose because, far from reducing the amount of water required for 
a given consistency they have had precisely the opposite effect. This 
situation has been summarized by Mr. F. R. McMillan: — 2 

"It can be stated as a general rule that an increase in the necessary 
water content of the cementing paste in concrete is detrimental. It 
follows, therefore, that any beneficial effect which an admixture may 
have must compete with the detrimental effect of any increase in the 
water content which its use may incur. This holds for portland cement 
as well as for other powdered materials. For example, to add 
cement only to the mix will increase the strength to a greater degree 
than to add the same amount of cement together with water. The fact 
that the addition of cement plus water may show an increase in strength 
merely illustrates that the detrimental effect of the added water did 
not offset the beneficial effect of the added cement/' 

The many expedients which have been tried, whether production 
of special cements by altering the composition of the cement itself or 
additions to the cement or the mix, have produced, in many cases at 
least, desirable results in some particular direction. They have not, 
however, been effective in attacking the underlying cause of most of 
the weakness of concrete or mortar; the excess water required to make 
the mix placeable. It would appear that any radical improvement in 
the properties of concrete or mortar should be sought in the reduction 
of this 'placing' water. Actually much of the investigational work on 
concrete has been direct to this end through mix design, selection of 
materials, methods of handling and similar means. As pointed out by 
Mr. McMillan 3 the benefits to be derived by these expedients are small : — 

"At best, only a bare 5 per cent of the concrete volume in plastic 
mixtures can be changed from water into solid material by improve- 
ments in grading over what is ordinarily accomplished. This leaves 
from 8 to 12 per cent of water, as shown in the figures. It is toward 
the reduction of this quantity of water that any proposed improvements 
must be directed." 

Accepting cements as they are now produced and assuming that 
every available advantage has been taken of the best methods of mix 
design and concrete handling, there still remains a wide gap between 
the properties of the concrete produced and the potential optimum. 
The most promising approach to a means of closing this gap lies in a 
study of the water-cement paste as a colloidal system and the applica- 
tion to it of physico-chemical principles, particularly that of dispersion. 



2 A Method of Evaluating Admixtures by F. R. McMillan and T. C. Powers 

J. Am. Con. Inst., April, 1934. 
3 Basic Principles of Concrete Making — By F. R. McMillan, Pg. 65. 

[5] 



DISPERSION IN A LIQUID MEDIUM 

When incorporated in an aqueous medium the particles of a solid 
tend to agglomerate and act as large clumps rather than as individual 
particles Fig. 1 . This is known as a flocculated condition and is due 
to the absence of electrostatic charges on the particles so that when 
they collide they tend to stick together. If a dispersing agent is incor- 
porated in the "flocculated solid-liquid system then the agglomerates 
or clumps tend to be broken up and the solid particles are distributed 
more or less evenly through the aqueous medium in the form of 
individual or discrete particles. The system is then said to be defloccu- 
lated or dispersed (Fig. II . The action of the dispersing agent is 
caused by its orientation with respect to the solid particles whereby 
these are" endowed with electrostatic charges of like sign so that when 
they collide they are mutually repelled and do not tend to stick together. 
This effect may also be enhanced by the action of the dispersing 
agent as a protective colloid which prevents the particles coming in 
close contact with one another. 



Fig. I. 



Pig. II. 



« 


8 ^«£ 




°00 00 ° O 

o o ° o o o ° 

o o o o 
c ° _ o o o 
a ° o 
° o o o ° ° 




Flocculated 




Dispersed 



Dispersing agents are specific in their nature, that is, a dispersing 
agent for one solid-liquid system may or may not be a dispersing agent 
for some other liquid-solid system. What reagent or reagents will act 
as dispersing agent for one particular system depends on the absorption 
relations between the dispersing agent and the system and will be 
determined by experiment. Dispersing agents, moreover, should not 
be confused with wetting agents, emulsifying agents and other surface 
active compounds*. Wetting agents are compounds which reduce the 
surface tension of water and thereby reduce the interfacial tension 
between the water and the solid which is to be wet. Emulsifying agents 
are compounds which concentrate at the interface between the con- 
tinuous and the emulsified or dispersed phase due to the solubility 
relations of the two parts of the molecule. While these reagents may 
appear to have some of the characteristics of dispersing agents they 
are not dispersing agents and do not produce the same results. Further- 
more, these wetting and emulsifying agents tend to cause foaming and 
may introduce other extraneous effects in any particular system. 

•Fig. Ill— (See pag 



[6] 



Fig. Ill 






~4— In tube containing the 
foaming agent, note form- 
ation of a stable foam, 
which is absent in tube 
containing the dispersing 
agent. — >- 

In this manner the foaming 
agent introduces a large 
quantity of air into the mix. 





- 



■ 



Foaming Agent 



Dispersing Agent 



171 



DISPERSION OF PORTLAND CEMENT 



The operation of dispersing agents has been known and utilized for 
a long time with respect to some applications as for example, in the 
ceramic industries for the deflocculation of clay slips. Until recently 
no dispersing agents have been known which were applicable to the 
deflocculation of portland cement. Recent researches have shown that 
certain complex organic compounds will disperse cement and will not 
have injurious effects such as a marked lowering of surface tension caus- 
ing foaming or interference with the hydration reactions of the cement. 

The action of a cement dispersing agent on portland cement in 
water is similar in its effects to the action of any dispersing agent in 
a solid-liquid system. Fig. IV shows photomicrographs (a) of cement 
in water in its normal or flocculated condition and (b) of cement in 
the dispersed condition, produced by adding a small amount of dis- 
persing agent to the water. 

Fig. IV 




Undispersed 



DlSPEKSKD 



The dispersion or deflocculation of portland cement in a concrete 
or mortar mix is important in a number of aspects. In general it may 
be pointed out that the reactions on which portland cement depends 
for its valuable properties are surface reactions. They are, therefore, 
a function of the surface area of the cement. For this reason cement 
manufacturers have consistently increased the fineness of grinding of 
cement clinker. Unfortunately the full surface area produced by fine 
grinding is not available for reaction due to the flocculated condition 
of the cement in the mix. It is perhaps even more unfortunate that 
this agglomerating tendency is even greater with greater fineness so 
that the beneficial effects of fine grinding have been in some measure 
offset by the formation of clumps. The addition of a dispersing agent 
to portland cement mixes has made available for reaction for the first 
time the full surface area of the cement particles. A dispersing agent 
in a cement mix, therefore, permits utilization of the cement to the 
full extent. 












[8] 



A special Held is that of colored concrete or mortar mixes. To pro- 
duce color in a concrete structure suitable pigments are incorporated 
in the mix with the cement and in some cases colored aggregates are 
used. In such an application a cement dispersing agent offers not only 
advantages in relation to the properties of the co \r mortar but 

it also effects improvements with respect to the pigment itself. The 
ence of the dispersing agent facilitates the dissemination of the 
pigmenl uniformly throughout the mix, increases the brilliance of the 
resulting color, ; equal color with less pign ei • poration 

of any fines including pigments has an adverse effect on the properties 
of the mortar since the water requirement of the mix is in< 
and overcomes rh«- deleterious effects of man' 



f 




**~ Color without dispersing 
l settles rapidly in 
flocculated condition. 

Dispersed color remains 
ipended — ► 




Undispersed 
Color 



Dispi 
Coi 



EFFECTS OF DISPERSION ON THE PROPERTIES OF 
CONCRETE AND MORTAR 

Since the properties of concrete and mortar are primarily dependent 
on the amount and quality of the cement paste any influence which 
alters the nature of this paste will inevitably influence the properties 
of the mix Dispersion of the cement basically changes the relations 
of the solid particles to the liquid in this colloidal system and conse- 
quently may be expected to have a profound influence on many if not 
all of the characteristics of the concrete or mortar. These effects may 
be divided into two groups corresponding to the two states in which 
concrete exists: the transitory plastic stage during placing and the 
ultimate hardened mass. 

^—Effects of Dispersion During Plastic Stage 

The plastic state is vitally important because this is the period 
during which the concrete or mortar is placed to fill the space which 
it is to occupy, compacted, and finished. Unless the mix is workable 
at this time, a sound structure will not be produced regardless of any 
other properties of the mix. This property of workability may be 
considered as made up of two components: mobility or ease of flow and 
cohesiveness or resistance to segregation. 

Dispersion of the cement particles will increase mobility or ease of 
flow. This is because the water held in the clumps or agglomerates ot 
the flocculated cement is released to become a part of the fluid medium 
through which the particles move. Further by breaking up these 

Fig. VI 




UNTREATED MIX 

6 ' _- gals. 

1 in .__ 



DISPERSED MIX 

Slump 5 in. 



110] 



clumps the size of the units in the liquid is reduced so that thev can 
move more easily past each other in the fluid. The result is a 'more 
workable concrete which is more easily handled, or placed with less 
danger of the defects commonly due to lack of workability. What is 
perhaps even more important is that this permits a more workable mix 
to be produced with less water, that is, at a lower water cement ratio. 

Cohesiveness is attributable to the attractive forces between sur- 
faces. 1 herefore. dispersion of the cement which makes available a 
greater surface area will increase the cohesiveness of the mix*. \ first 
result is that the mix becomes more "fatty" or "buttery" which is 
extremely important in some types of work. An even more generally 
important effect is a reduction of the tendency of the components of 
the mix to separate, that is, toward segregation. The aggregate is less 
apt to separate from the cement paste so that the danger of honey- 
combing, sand streaking and similar defects is minimized. In its 
upward movement through the mix the water tends to collect under 
the larger pieces of aggregate forming pockets on the underside such 
that the aggregate is not bonded to the cement paste. The pockets 
constitute points of weakness and of attack by destructive agencies. 
Separation of the water and fines in an upward direction from the 
coarser part of the mix is prevented. By this means 'bleeding' or 
watergain and the formation of laitance are eliminated or reduced. 
1 he uniformity of the mix in place is enhanced. (Fig. VII— see page 12). 

A further effect of dispersion, also due to the greater surface area 
available, is a greater force holding the water to the cement particles. 
1 his produces higher "water retentivity" which is particularly impor- 
tant in masonry mortars where porous masonry units tend to suck water 
out of the mortar. It is also important in other mortars and concrete as 
it retains the water in the mass promoting better curing. 

One phenomenon which occurs in concrete and mortar during the 
plastic stage has been rather neglected. This is the volume change or 
more specifically shrinkage which occurs before hardening. The volume 
changes which occur at this time are in all probability more important 



0) This does not contradict the previously made statement 
that the dispersion of the cement particles is due to the 
repellent action of like electrostatic charges. This repul- 
sion which effects dispersion refers to the forces between 
the cement particles. The attraction which operates in 
connection with cohesiveness refers to the forces between 
the cement particles and the other components of the mix, 
particularly the aqueous medium in which the cement 
particles are dispersed. Since the water does not carry 
an electrostatic charge there is no repulsion between it 
and the cement particles: hence the attractive forces 
between the water and the solids in the mix are dependent 
on surface area of the solids. 



[11] 









Fig. VII 




<— In the flocculated con- 
dition the solid particles 
settle to the bottom leaving 
clear uater at the top; 
a condition analogous to 
water gain. 

The dispersed particles 
remain suspended. — ►" 



Untreated i Flocculated 



Treated (Dispersed) 









than those which take place subsequently 2 . They are caused by move- 
ment of water from one part of the mix to another and by loss of water 
from the mix by suction, by evaporation or by other means. Such 
volume changes produce incipient or actual cracks which impair the 
integrity of the structure and make it susceptible to subsequent attack. 
( Fig. VIII). Dispersion of the cement counteracts these volume changes, 
first by reducing the amount of water required for a workable mix and 
second by imparting higher water retentivity thus resisting movement 
and loss of water. 

Fig. VIII 



Photomicrographs 
show how cracks 
due to shrinkage 
open wider and 
new cracks appear 
with application 
of loads. 





CRACKS IN UNSTRESSED CONDITION 



CRACKS WHEN LOAD IS APPLIED 



( 2 ) "The occurrence of cracks during the 'pre-set' period is so 
frequent, especially in flat work, it is surprising suclvlittle 
mention has been made of it in concrete literature. Yet 
positive, or even incipient, cracks produced in this pre-set 
period are often more dangerous to continuity than those 
produced by the normal drying out after the cement has 
become hard set. 

When screeding of flat work or rodding and vibration 
of concrete in forms is completed, all solid particles settle 
slowly at a uniform rate until the coarser particles become 
arched and fixed in the mass. Each smaller size will then 
stratify until it in turn touches other particles. This 
settling action exposes water at the surface which proceeds 
to evaporate in the presence of dry air, warm weather, and 
wind, singly or combined. The structure formed by the 
settlement of the solids to a rigid condition is rather loose 
and the smaller particles are still far from consolidated, 
being held apart by the water films on their surfaces. 

As the mixture dries out, the contained water moves 
through the mass to the drying surfaces and may cause 
further readjustments. When drying has proceeded 
beyond the point of particle adjustment, air is drawn 
into the mass to replace the volumes in the voids formerly 
filled with water. From this stage on to the final drying 
or to some point before hard set, surface tension plays 
its part in the shrinkage of the mass." 

C. A. G. Weymouth— J. Am. Con. Inst., Sept., 1940, Supplement Section 1. 



Pg. 540-2 



Pg. 540-3 



[13] 






The effects of dispersion of the cement particles on plastic concrete 
or mortar may be summarized as follows:— 

1. More placeable concrete with less water. 

2. Increased fattiness. 

3. Reduced segregation and bleeding. 

4. Greater water retentivity. 

5. Reduced shrinkage before hardening. 






B .— Effects of Dispersion on Hardened Concrete or Mortar 

Dispersion affects practically all the important properties of the 
hardened concrete or mortar. This is due primarily to two causes. 
First, the reduction of the amount of water required in the mix pro- 
duces the well-known beneficial effects of reduced water-cement ratio 
and reduced water per unit volume. (Fig. IX). Second, the dispersion 
of the cement particles produces a finer grained structure in the cement 
paste and an increased surface area such that the hydration reactions 
of the cement will proceed more effectively and more efficiently. Some 
of the more important properties may be considered in somewhat 
more detail. 

IX 










UNTREATED MIX 




DISPERSED MIX 


- 




4' 2 gals. 




.. Slump 


- 






Durability — Durability means the ability of the structure to 
resist destructive agencies. These are commonly corrosive solutions 
and freezing and thawing. Since the attack of corrosive solutions is 
a reaction occurring at the surface where the solution comes in contact 
with the cement the rapidity of attack is dependent primarily on the 
ability of the corrosive solution to penetrate into the structure, second- 
arily, on the ability of the cement itself to resist attack. The ability of 
the solution to penetrate is governed by the same factors which con- 
tribute to watertightness. Hence, a dispersing agent increases resistance 
to corrosion. (Fig. X). 



Fig. X 



Corrosion tests on 1 :3 standard sand 
mortars, cured 7 days. Cylinders show 
result o£ 6 months 1 immersion in 8% 
Magnesium sulphate. 




[15] 



Disintegration by freezing and thawing is also primarily dependent 
on the ability of water to penetrate into the concrete where it will 
freeze, expand and break down the structure, secondarily, on the 
strength of the cement paste to resist this force. Since a dispersing 
agent reduces permeability and in other ways makes the concrete more 
water-tight and since it also increases strength, it will markedly increase 
resistance to freezing and thawing. (Fig. XI.; 

Fig. XI 







Untreated Concrete - 150 Cycles of Freezing and Thawing, 
Loss in Weight - 




te, Same Design and Consist] 

\i> Thawing - Lose m weioh-i - 101 



WaL 8 Watertightnese is dependent on freedom from 

-edom from cracks and on permeability. Since the 
A a disp< - ent, as previously discussed, results in an impi 

ment in all these respects it will increase watertight!.' 






[16] 



A 



Irength Stre 

ngth will be incn 
h ipenuon I 
lead i to 
menl in tren •' I 

Flfi XI] 



































































• 























. 





























































































proportional to I he 

The reduction ii 
by the u i 



absorption 



Mil 















• 




































































































J 



I 






Volume Change — Volume change or shrinkage is proportional 
to the volume of cement paste per unit volume of concrete, that is, 
the volume of cement plus the volume of water. Reduction in the 
water then reduces volume change. 

Uniformity -The uniformity of the hardened structure and 
freedom from gross defects will be improved due to the improvement 
in the properties of the plastic mix as described previously. 

The effects of a dispersing agent on the properties of the hardened 
concrete or mortar may be summarized as follows: - 

1. Increased durability and longer life. 

2. Increased watertightness. 

3. Higher strength. 

4. Lower volume change. 

5. Lower permeability or absorption. 

6. Greater uniformity and freedom from gross defects. 



CONCLUSION 

The basic reason that concrete and mortar do not realize the full 
potential qualities which are warranted by the inherent characteristics 
of portland cement lies chiefly in the excess water required for place- 
ability. Any improvements to be expected in the properties of concrete 
will naturally follow from methods which permit this excess water 
to be reduced. An attack on this problem has been made from the 
point of view of a study of the physico-chemical characteristics of the 
cement-water paste. The result of this work has been the application 
of the principle of dispersion to the system. 

A cement dispersing agent radically alters the physical nature of 
the paste in such a manner that placeability can be attained in concrete 
and mortar with a substantial reduction in the water required. This 
in turn has profound effects with respect to improvement of durability, 
watertightness, strength, volume change and other properties. 

It will be realized that this principle of cement dispersion is applic- 
able to concrete and mortar generally. Since the many applications of 
cement mixes require some variations in the properties of the different 
mixes, some modifications of or additions to the cement dispersing 
agent may be desirable, but the principle of reduction in water by 
means of dispersion will remain universally beneficial wherever 
cement is used. 

Master Builders Research Laboratories 
Cleveland, Ohio 






MASTER BUILDERS 

PRODUCTS EMPLOYING 

THE 

CEMENT DISPERSION PRINCIPLE 

The principle of dispersion of cement is applicable to any type of 
work involving cement in mortar or concrete. This work is of a very 
varied nature and for different applications somewhat different proper- 
ties are required. To accomplish this purpose the cement dispersing 
agent may be combined with other basic principles for the improvement 
of specific properties of concrete and mortar, as illustrated by the 
diagram below. These include pozzuolanic activity, stearate water- 
proofing, chemical hardening, and metallic aggregates. 

The Master Builders Company has developed a group of products 
adapted to various specific concrete and mortar applications. The 
exclusive dispersing agent is incorporated in each of these products 
in a manner to impart the maximum effect on the resultant structure. 
These products are as follows: 



Application 

( oncrete (General) 

High Early Strength Concrete 

Concrete (Exposed to Capillary 

Moisture) 
Moors — Heavy Duty 
Floors - Light Duty 
i olored Floors 

k Mortar 

Colored Brick Mortar 

tuting and Maintenance 



Product 

Pozzolith 

High Early Pozzolith 

Omicron Waterproofing and Stearox 

Masterplate 

Mastermix 

Colored Metalicron and Colormix 

Omicron Mortarproofing ("O. M/') 

Colored Omicron Mortarproofing 

Emheco and Metallic Waterproofing 



PRODUCT COMPOSITION DIAGRAM 



CfMfNT 

QtSPfMSMG AcrtOH 

Pi4sr/cjmfG 
Watca ftevucTton 

][ 



METALLIC 
AGGREGATE 

Sti&NkAGE 
CONTROL 





THE MASTER BUILDERS COMPANY 



Factories in Cleveland 
and Buffalo 



CLEVELAND, OHIO 



Sales Offk. 
All Principal Citie*